Active and passive electrical properties of single bullfrog atrial cells.

Abstract

Single cells from the bullfrog (R. catesbeiana) atrium were prepared using a modification of the enzymatic dispersion procedure described by Bagby et al. Visualization of relaxed cells via phase-contrast or Nomarski optics (magnification, 400-600) indicates that cells range between 150-350 .mu.m in length and 4-7 .mu.m in diameter. The mean sarcomere length in relaxed, quiescent atrial cells is 2.05 .mu.m. Conventional electrophysiological measurements were made. In normal Ringer''s solution (2.5 mM K+, 2.5 mM Ca2+) acceptable cells have stable resting potentials of .apprx. -88 mV, and large (125 mV) long-duration (.apprx. 720 ms) action potentials can be elicited. The Vm membrane potential vs. log[K+]0 relation obtained from isolated cells is similar to that of the intact atrium. The depolarizing phase of the action potential of isolated atrial myocytes exhibits 2 pharmacologically separable components: tetrodotoxin (10-6 g/ml) markedly suppresses the initial regenerative depolarization, whereas verapamil (3 .times. 10-6 M) inhibits the secondary depolarization and reduces the plateau height. A bridge circuit was used to estimate the input resistance (220 .+-. 7 M.OMEGA.) and time constant (20 .+-. 7 ms) of these cells. Two-microelectrode experiments revealed small differences in the electrotonic potentials recorded simultaneously at 2 different sites within a single cell. The equations for a linear, short cable were used to calculate the electrical constants of relaxed, single atrial cells. This preparation may be particularly suitable for voltage-clamp studies.