Ca2+ channel modulation by 8-bromocyclic AMP in cultured heart cells.

Modulation of ion channels is of increasing interest as it is an important step in the regulation of cellular functions. We have analysed the effect of 8-bromocyclic AMP on Ca2+ channels in cultured cardiac cells by the patch-clamp method and report here that there was a large increase in the probability of opening of the channels. On the basis of a recently proposed kinetic reaction scheme we suggest that cyclic AMP-dependent phosphorylation of Ca2+ channels primarily promotes the forward rate constants which lead to the open state of a Ca2+ channel during depolarization.

Sodium channels in cultured cardiac cells.

Primary cardiac cell cultures were prepared from the hearts of neonatal rats. The patch-clamp method (Hamill, Marty, Neher, Sakmann & Sigworth, 1981) was applied for studying whole-cell Na+ currents and single-channel Na+ currents, respectively. Whole-cell recordings yielded voltage- and time-dependent Na+ currents which could be blocked by tetrodotoxin.

Modulation by intracellular ATP and cyclic AMP of the slow inward current in isolated single ventricular cells of the guinea-pig.

Effects of ATP and of cyclic AMP on membrane current systems were investigated in isolated single ventricular cells from guinea-pig hearts by applying the suction electrode method. The intracellular milieu was dialysed with various solutions which were perfused continuously through the suction pipette. The presence of ATP, cyclic AMP and EGTA in the perfusion solution kept the plateau phase of the action potential almost intact for as long as 30 min.

Membrane currents in the rabbit atrioventricular node cell.

The rabbit A-V node was dissected into pieces (0.2 x 0.2 x 0.

Ionic mechanism underlying muscarinic acetylcholine response in the rabbit sinoatrial node.

1. The clusters composed of 10-20 cells of the rabbit sinoatrial node were prepared by coronary perfusion of collagenase and their response to ionophoretic application of ACh was recorded. The hyperpolarizing response showed a sigmoidal onset without any clear latency when the ACh pipette was positioned close to the cell surface.

Spontaneously active cells isolated from the sino-atrial and atrio-ventricular nodes of the rabbit heart.

Single cells or cell clusters composed of 3-10 cells were isolated from the S-A and A-V nodes of the rabbit heart by coronary perfusion of collagenase dissolved in Ca-free Tyrode solution (0.04%, for 1 hr). For comparison, atrial and ventricular cells were also isolated from the same heart.

Kinetics and rectification of the slow inward current in the rabbit sinoatrial node cell.

The slow inward current (is) in the rabbit sinoatrial node cell was studied by the conventional two-microelectrode voltage clamp technique. When is was measured as the difference between two records obtained before and after blocking is with D 600, the fully activated current (is)-voltage relation was non-linear; the conductance decreased in the negative potential range resulting in an almost constant amplitude of is negative to -10 mV. The degree of steady-state activation was about 1 at -5mV and 0 at -65mV.

The spontaneous action potential of rabbit atrioventricular node cells.

The rabbit atrioventricular (A-V) node, with dimensions of approximately 5 X 3 mm was dissected into 15 small specimens (0.5 X 0.5 mm).