EFFECTS OF NERVE-STIMULATION ON THE SPONTANEOUS ACTION-POTENTIALS RECORDED IN THE PROXIMAL RENAL PELVIS OF THE GUINEA-PIG

The effects of nerve stimulation on the electrical and mechanical acti vity of the smooth muscle of the proximal renal pelvis of the guinea-p ig were investigated using standard tension and microelectrode recordi ng techniques. Spontaneous action potentials were deemed to have been recorded from three cell types: (1) ''pacemaker'' cells (9 of >120) ha d membrane potentials (MPs) of -42.1+/-2.9 mV and fired action potenti als of a simple waveform; (2) ''driven'' cells (>100) had more stable MPs of -56.1+/-1.2 mV (n = 36) and more complex ''ureter-like'' action potentials; (3) the remaining cells had MPs of -45.5+/-1.7 mV (n = 15 ) and action potentials with a waveform ''intermediate'' to groups (1) and (2). Nifedipine (0.1-1 mu M) and Cd2+ (0.1-1 mM) blocked all spon taneous action potential discharge and depolarized the membrane to nea r -40 mV. Intramural nerve stimulation (10-50 Hz for 1-10 s) increased both the amplitude and frequency of the spontaneous contractile activ ity, this increase peaked in about 30 s and decayed slowly over severa l minutes. Nerve stimulation depolarized pacemaker and driven cells 9. 1+/-3.5 (n = 3) and 1.6+/-0.7 (n = 6) mV, respectively; the frequency of their action potential discharge increased from 7.6+/-2.7 and 9.9+/ -1.1/min to 17.3+/-0.5 and 11.1+/-1.4/min, respectively. The duration of the action potentials in driven cells also increased significantly for several minutes. All these effects were blocked by tetrodotoxin (T TX) (1.6 mu M) It was concluded that the positive chronotropic and ino tropic effects of nerve stimulation on renal pelvis contractility can be correlated with the changes in the frequency and duration of the ac tion potentials recorded in driven cells.