AJP - Cell Physiology, Vol 257, Issue 4 C802-C809, Copyright © 1989 by American Physiological Society
Passively propagated spikes from the soma of cells in pineal gland of guinea pigs
H. C. Parkington, H. A. Coleman and I. McCance
Department of Physiology, Monash University, Clayton, Victoria, Australia.
The membrane properties of cells within the pineal gland of guinea pigs
were studied using intracellular electrophysiological techniques. The
electrotonic responses to intracellular current injection decayed with a
single exponential in approximately 60% of cells but was preceded by a
quicker component in the remainder. The membrane time constant was 2.8 ms.
Depolarization beyond -29 mV activated an outward current that reversed at
around the value of the resting potential. Hyperpolarization activated a
slow inward current. Spikes occurred in response to activation of
alpha-adrenoceptors. They were resistant to tetrodotoxin but were abolished
by nifedipine and verapamil, suggesting that calcium carries the current
during their upstroke. Spikes could not be evoked by depolarizing current
pulses of 1-ms to 2-s duration. The responses to hyperpolarizing current
steps or voltage-clamp steps applied during the peak of spikes evoked by
nerve stimulation were indistinguishable from the responses to those
applied between spikes. During nerve stimulation, fluctuations were
observed in the current trace of cells under voltage clamp, indicating that
the spikes could not be voltage clamped successfully. It is concluded that
the spikes occurring in response to nerve stimulation are generated on the
processes of the pinealocytes and are passive in the soma.
