Ca2+ Current in Rabbit Carotid Body Glomus Cells is Conducted by
Multiple Types of High Voltage-Activated Ca2+ Channels
Jeffrey L. Overholt and Nanduri R. Prabhakar
Department of Physiology and Biophysics, Case Western Reserve University
Cleveland, OH 44106-4970, Telephone (216) 368-8962
Fax: (216) 368-1693,
APStracts 4:0094N, 1997.
ABSTRACT
Carotid bodies are sensory organs that detect changes in arterial oxygen.
Glomus cells are presumed to be the initial sites for sensory transduction,
and Ca2+-dependent neurotransmitter release from glomus cells is believed to
be an obligatory step in this response. Some information exists on the Ca2+
channels in rat glomus cells. However, relatively little is known about the
types of Ca2+ channels present in rabbit glomus cells, the species in which
most of the neurotransmitter release studies have been performed. Therefore,
we tested the effect of specific Ca2+ channel blockers on current recorded
from freshly dissociated, adult rabbit carotid body glomus cells using the
whole cell configuration of the patch clamp technique. Macroscopic Ba2+
current elicited from a holding potential of -80 mV activated at a Vm of ÷-30
mV, peaked between 0 and +10 mV, and did not inactivate during 25 ms steps to
positive test potentials. Prolonged (÷2 minutes) depolarized holding
potentials inactivated the current with a V1/2 of -47 mV. There was no
evidence for T-type channels. On steps to 0 mV, 6 mM Co2+ decreased peak
inward current by 97ñ1%. 2 æM nisoldipine, 1 æM -conotoxin GVIA and 100 nM -
agatoxin IVa each blocked a portion of the macroscopic Ca2+current (30ñ5, 33ñ5
and 19ñ3% after rundown correction, respectively). Simultaneous application
of these blockers revealed a resistant current that was not affected by 1 æM -
conotoxin MVIIC. This resistant current constituted 27ñ5% of the total
macroscopic Ca2+ current. Each blocker had an effect in every cell so tested.
However, the relative proportion of current blocked varied from cell
to cell. These results suggest that L, N, P and resistant channel types each
conduct a significant proportion of the macroscopic Ca2+ current in rabbit
glomus cells. Hypoxia- induced neurotransmitter release from glomus cells may
involve one or more of these channels.
Received 28 March 1997; accepted in final form 5 June 1997.
APS Manuscript Number J260-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997