{"id":40542,"date":"2020-09-25T19:36:35","date_gmt":"2020-09-25T14:06:35","guid":{"rendered":"https:\/\/johnsonfrancis.org\/professional\/?p=40542"},"modified":"2020-09-25T19:36:35","modified_gmt":"2020-09-25T14:06:35","slug":"cardiac-action-potential","status":"publish","type":"post","link":"https:\/\/johnsonfrancis.org\/professional\/cardiac-action-potential\/","title":{"rendered":"Cardiac action potential"},"content":{"rendered":"<h2><span style=\"color: #008000;\">Cardiac action potential<\/span><\/h2>\n<p><iframe loading=\"lazy\" width=\"560\" height=\"315\" src=\"https:\/\/www.youtube.com\/embed\/8ffs-KSDOM4\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture\" allowfullscreen=\"\"><\/iframe><br \/>\nTypically described cardiac action potential is that of the myocardial cell. Action potential of tissues like sinus node will be different and characterized by <em>diastolic depolarization<\/em> which contributes to the automaticity.<\/p>\n<p><strong>Action potential of the myocardial cell<\/strong><\/p>\n<p>It may be noted that the cardiac action potential is different from the surface electrocardiogram which represent the sum total of all electrical activity of the heart as recorded from the body surface. Myocardial action potential is recorded with intracellular electrode under experimental conditions. The action potential has a total of 5 phases.<\/p>\n<p><em>Phase 0 (Rapid depolarization): <\/em>Phase 0 is the initial phase of rapid depolarization in which the intracellular voltage rises from about -90mV to about +20 mV. The peak rate of rise is called V<sub>max<\/sub>. It is due to the rapid influx of sodium ions through the open sodium channels (I<sub>Na<\/sub>).<\/p>\n<p><em>Phase 1 (Notch): <\/em>Phase 1 is the rapid initial fall in intracellular voltage due to open potassium channels (I<sub>to<\/sub> \u2013 transient outward current).<\/p>\n<p><em>Phase 2 (Plateau):<\/em> Phase 2 is a plateau phase in which influx of calcium ions through L-type calcium channels (I<sub>Ca-L<\/sub>) is balanced by efflux of potassium ions by slow delayed rectifier current (I<sub>KS<\/sub>).<\/p>\n<p><em>Phase 3 (Repolarization):<\/em> In phase 3, calcium channels close while potassium channels remain open till the intracellular voltage reaches the baseline value of -90mV. The potassium channels active in this phase are I<sub>KS<\/sub>, I<sub>KR<\/sub> (rapid delayed rectifier current) and I<sub>K1<\/sub> (inward rectifier current).<\/p>\n<p><em>Phase 4 (Diastole):<\/em> Phase 4 is the resting membrane potential which is maintained stable at -90mV by the potassium currents (I<sub>K1<\/sub>). Sodium and calcium channels are closed during phase 4.<\/p>\n<figure id=\"attachment_40543\" aria-describedby=\"caption-attachment-40543\" style=\"width: 1200px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-40543\" src=\"https:\/\/johnsonfrancis.org\/professional\/wp-content\/uploads\/2020\/09\/action-potential.jpg\" alt=\"Action potential of ventricular myocardial cell\" width=\"1200\" height=\"684\"><figcaption id=\"caption-attachment-40543\" class=\"wp-caption-text\">Action potential of ventricular myocardial cell<\/figcaption><\/figure>\n<p><strong>Action potential of pacemaker cells<\/strong><\/p>\n<p>Action potential of the pacemaker cell is different from that of ventricular myocardial cell. It is characterized by lower slope of phase 0 (lower Vmax) and the presence of diastolic depolarization mediated by the <em>funny current<\/em> (I<sub>f<\/sub>), also known as <em>pacemaker current<\/em>. Funny current is through the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and is a mixture of sodium and potassium currents. With sympathetic stimulation, funny current and the slope of diastolic depolarization increases and heart rate increases. The slope of diastolic depolarization decreases with parasympathetic stimulation.<\/p>\n<p>The depolarization phase is mainly due to L-type calcium channels (I<sub>Ca-L<\/sub>). During repolarization, potassium channels open and calcium channels close. There is some contribution to the diastolic depolarization phase by T type calcium channels (I<sub>Ca-T<\/sub>).<\/p>\n<figure id=\"attachment_40545\" aria-describedby=\"caption-attachment-40545\" style=\"width: 1200px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-40545\" src=\"https:\/\/johnsonfrancis.org\/professional\/wp-content\/uploads\/2020\/09\/Action-potential-of-pacemaker-cells.jpg\" alt=\"Action potential of pacemaker cells\" width=\"1200\" height=\"682\"><figcaption id=\"caption-attachment-40545\" class=\"wp-caption-text\">Action potential of pacemaker cells<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Cardiac action potential Typically described cardiac action potential is that of the myocardial cell. Action potential of tissues like sinus node will be different and characterized by diastolic depolarization which contributes to the automaticity. Action potential of the myocardial cell It may be noted that the cardiac action potential is different from the surface electrocardiogram [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":40543,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","footnotes":""},"categories":[10],"tags":[114,115,1122,1557,1932,2018,2745,3227,3614,3822,3999],"class_list":["post-40542","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hbc","tag-action-potential-of-pacemaker-cells","tag-action-potential-of-ventricular-myocardial-cell","tag-diastolic-depolarization","tag-funny-current","tag-inward-rectifier-current","tag-l-type-calcium-channels","tag-pacemaker-current","tag-rapid-delayed-rectifier-current","tag-slow-delayed-rectifier-current","tag-t-type-calcium-channels","tag-transient-outward-current"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.9 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Cardiac action potential - All About Cardiovascular System and Disorders<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/johnsonfrancis.org\/professional\/cardiac-action-potential\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Cardiac action potential - All About Cardiovascular System and Disorders\" \/>\n<meta property=\"og:description\" content=\"Cardiac action potential Typically described cardiac action potential is that of the myocardial cell. Action potential of tissues like sinus node will be different and characterized by diastolic depolarization which contributes to the automaticity. Action potential of the myocardial cell It may be noted that the cardiac action potential is different from the surface electrocardiogram [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/johnsonfrancis.org\/professional\/cardiac-action-potential\/\" \/>\n<meta property=\"og:site_name\" content=\"All About Cardiovascular System and Disorders\" \/>\n<meta property=\"article:published_time\" content=\"2020-09-25T14:06:35+00:00\" \/>\n<meta name=\"author\" content=\"Johnson Francis\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Johnson Francis\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/cardiac-action-potential\\\/#article\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/cardiac-action-potential\\\/\"},\"author\":{\"name\":\"Johnson Francis\",\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/#\\\/schema\\\/person\\\/5441d907049b914770f4bd98fb57feec\"},\"headline\":\"Cardiac action potential\",\"datePublished\":\"2020-09-25T14:06:35+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/cardiac-action-potential\\\/\"},\"wordCount\":414,\"publisher\":{\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/#\\\/schema\\\/person\\\/5441d907049b914770f4bd98fb57feec\"},\"image\":{\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/cardiac-action-potential\\\/#primaryimage\"},\"thumbnailUrl\":\"\",\"keywords\":[\"Action potential of pacemaker cells\",\"Action potential of ventricular myocardial cell\",\"diastolic depolarization\",\"Funny Current\",\"inward rectifier current\",\"L-type calcium channels\",\"Pacemaker current\",\"rapid delayed rectifier current\",\"slow delayed rectifier current\",\"T type calcium channels\",\"transient outward current\"],\"articleSection\":[\"HBC\"],\"inLanguage\":\"en-US\"},{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/cardiac-action-potential\\\/\",\"url\":\"https:\\\/\\\/johnsonfrancis.org\\\/professional\\\/cardiac-action-potential\\\/\",\"name\":\"Cardiac action potential - 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