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 activity of the smooth muscle of the proximal renal pelvis of the guinea-pig were investigated using standard tension and microelectrode recording techniques. Spontaneous action potentials were deemed to have been recorded from three cell types. (1) pacemaker cells (9 of >120) had membrane potentials (MPs) of -42.1±2.9 mV and fired action potentials 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 M) and Cd²⁺ (0.1–1 mM) blocked all spontaneous action potential discharge and depolarized the membrane to near -40 mV. Intramural nerve stimulation (10–50 Hz for 1–10 s) increased both the amplitude and frequency of the spontaneous contractile activity, this increase peaked in about 30 s and decayed slowly over several 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 (TTX) (1.6 M). It was concluded that the positive chronotropic and inotropic effects of nerve stimulation on renal pelvis contractility can be correlated with the changes in the frequency and duration of the action potentials recorded in driven cells.