Membrane properties and discharge characteristics of rat intracardiac neurones in vitro: the effect of temperature
The membrane properties of neonatal rat intracardiac neurones were investigated at room temperature (24-26 TC) and at 35-37 °C using the perforated patch technique (Horn & Marty, 1988). Neurones had a mean resting membrane potential (Em) of -51.3 ± 1.0 mV (meanj± S.E.M., n = 12) and -52.7 ± 1.1 mV (n = 7) at 25 and 37 TC, respectively. The mean input resistance was 1302 ± 367 MQ (n = 6) at 25 TC, comparable to values recorded using the whole-cell technique. The input resistance was on average 64 % less at 37 °C, but was not statistically significantly different from that measured at room temperature. Hyperpolarizing pulses induced time-dependent rectification in all neurones at both temperatures. In most neurones, depolarizing currents evoked firing of multiple, adapting, action potentials at 25 TC, the number of which increased with current strength (+50 pA, 1 s pulse producing a median discharge of 6 (range 1-13, n = 6)); this was attenuated at 37 °C to a median of 1 (range 0-2, n = 4, P < 0.03; t test). These results demonstrate marked differences in the discharge activity and response to hyperpolarizing currents from those obtained using the whole-cell, dialysed, patch technique under otherwise comparable recording conditions at room temperature (Xu & Adams, 1992). Moreover, these firing characteristics are altered by temperature.