Purpose: The role of various K+ channel populations in determining the time course and amplitude of the spontaneous action potentials and contractions in the smooth muscle cells of the guinea pig renal pelvis were investigated by standard electrophysiological and tension recording techniques.
Materials and methods: Electrical recordings in the proximal renal pelvis were used to demonstrate the presence of 3 cell populations based on the waveform of their Ca(2+)-dependent action potentials which we have termed "pacemaker," "intermediate" and "driven" action potentials.
Results: Blockade of large conductance (BK) or small conductance (SK) Ca(2+)-activated K+ channels with charybdotoxin (30 to 60 nM.) and tetraethylammonium (TEA) (0.5 to 2 mM.) or apamin (200 nM.) increased the duration of the action potentials recorded in "driven" cells. Tetraethylammonium (2 mM.) and 4-aminopyridine (2 mM.) increased the frequency of action potential discharge in both "driven" and "pacemaker" cells, as well as having a positive inotropic and chronotropic effect on the spontaneous contractions of the renal pelvis. In contrast, glibenclamide (0.1 to 1 microM.), Cs2+ (1 mM.) and Ba2+ (100 microM.) had little effect on either the contractile or electrical activity of the renal pelvis.
Conclusion: It was concluded that the frequency of contraction in the proximal renal pelvis is determined by the frequency of action potential discharge in "pacemaker" cells. On the other hand, increases in the amplitude of pelvic contractions may well be correlated with membrane depolarization and/or increases in the duration of the action potentials recorded in "driven" cells.