Comparison of steady-state electrophysiological properties of isolated cells from bullfrog atrium and sinus venosus.
Single electrode whole cell voltage-clamp experiments and frequency domain analyses have been used to study and compare the K+ currents in enzymatically dispersed single cells from the atrium and the sinus venosus (pacemaker region) of the bullfrog heart. Admittance measurements made near the "resting' or zero-current potential yield data from which the equivalent circuit of each cell type may be obtained. Data from both atrial and pacemaker cells are well-fitted by a model consisting only of parallel resistance-capacitative elements, as predicted from their micro-anatomy. Neither of these amphibian cardiac cells contain a transverse tubule system (TT) and both have very little sarcoplasmic reticulum (SR). These results complement and extend two earlier investigations: (i) Moore, Schmid and Isenberg (J. Membrane Biol. 81:29-40, 1984) have reported that in guinea pig ventricle cells (which do contain an internal membrane system consisting of transverse tubules and a substantial SR) the SR may be electrically coupled to the sarcolemma; (ii) Shibata and Giles (Biophys. J. 45:136a, 1984) have shown that although bullfrog atrial cells have an inwardly rectifying background K+ current, IK1, pacemaker cells from the immediately adjacent sinus venosus do not. Data from admittance measurements also provide evidence that a TTX-insensitive inward Ca2+ current is activated in the pacemaker range of potentials.
D000200:Action Potentials; D000818:Animals; D016275:Atrial Function; D001464:Barium / Q000494:pharmacology; D004558:Electric Stimulation; D006321:Heart / Q000502:physiology*; D006325:Heart Atria / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008839:Microelectrodes; D011892:Rana catesbeiana
D001464:Barium