Effect of various stimulus parameters on electrically-induced catecholamine secretion by thin slices of bovine adrenal medulla.

We examined the role of various stimulus parameters in electrically-induced catecholamine secretion by thin slices of bovine adrenal medulla. The stimulus parameters examined were voltage, duration, pulse width, and frequency for square-wave monophasic pulses. As each was examined it was held constant at a selected value for the evaluation of subsequent stimulus characteristics. For 16 mm2 tissue slices, catecholamine secretion was approximately linearly related to stimulus voltage over the range 20--80 volts, with a threshold of 20 V. Increasing the voltage beyond 80 V did not enhance secretion. Similarly, catecholamine secretion was dependent upon the frequency of stimulation. For stimuli delivered at 50 V for a 10-sec interval there was a four-fold increase in secretion over the frequency range 10--100/sec. Increasing pulse width at a constant voltage (50 V) over the range 0.4--2.0 msec resulted in a four-fold increase in catecholamine secretion. For pulses of 50 V, 50/sec and 0.8 msec pulse width, secretion was dependent upon the duration of the stimulus. Enhanced secretion was evident for times as short as 2 sec; between 5 and 15 sec of stimulation catecholamine secretion was linearly related to stimulus duration. Over the range 2--15 sec there was a five-fold enhancement of secretion. Electrically-induced catecholamine secretion by slices was markedly dependent upon stimulus parameters. In general, it was enhanced by increasing voltage, stimulus duration, pulse width and frequency. For most experiments a good choice of stimulus parameters appears to be 50 V 10 sec duration, 0.8 msec pulse width delivered at a frequency of 50/sec. Maximizing all stimulus parameters resulted in a 17-fold enhancement of secretion.