Affiliation:
1. Departments of Zoophysiology and Physiology, University of Göteborg, Göteborg, Sweden and the Department of Physiology, University of Iceland, Reykjavik, Iceland
Abstract
The effects of variations in external K
+
and Ca
2+
concentrations on electrical and mechanical activity of the isolated rat portal vein were studied using a sucrose-gap technique. Spontaneous activity in normal Krebs solution consists of bursts of action potentials accompanied by phasic contractions. Moderate reduction in [K+]
o
results in slight hyperpolarization with decreased discharge frequency. Greater reduction or total removal of extracellular K causes a temporary increase in burst frequency. Graded increases in [K+]
o
from 6 up to 128 mM cause depolarization with an increase in discharge frequency and in contraction amplitude until [K+]
o
reaches a level of 6 to 7 times normal when spike potentials are abolished and a contracture develops. The relationship between membrance potential and log [K
+
]
o
indicates a relatively low permeability to K
+
. Increasing [Ca
2+
]
o
causes slight hyperpolarization, decreased burst frequency, increased burst duration and increased contraction amplitude. Reducing [Ca
2+
]
o
causes increased frequency of discharge and shortening of bursts, until single spikes appear, each preceded by a prepotential; thus the activity resembles that in cardiac pacemaker cells. In Ca
2+
-free solution, electrical and mechanical activity ceases within 10 to 15 min. Calcium is essential for activation of the contractile mechanism and for maintenance of spontaneous spike discharge.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Cardiology and Cardiovascular Medicine,Physiology
Reference23 articles.
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