The peptide CGRP increases a high-threshold Ca2+ current in rat nodose neurones via a pertussis toxin-sensitive pathway.
1. The whole-cell variation of the patch clamp technique was used to study the effect of calcitonin gene-related peptide (CGRP) on voltage-gated calcium currents in acutely dissociated rat nodose ganglion neurones and to determine if its effects were mediated via a guanine nucleotide binding (G) protein. 2. Both low- and high-threshold calcium current components were present in nodose ganglion neurones. CGRP had no effect on the isolated low-threshold current component. However, CGRP (1-1000 nM, ED50 = 50 nM) caused a concentration-dependent increase in high-threshold calcium currents. CGRP (1 microM) increased the peak of these calcium currents 21 +/- 4% over controls. 3. CGRP enhanced a transient high-threshold calcium current evoked from a holding potential of -80 mV but did not affect the slowly inactivating high-threshold current evoked from -40 mV. Multiple high-threshold calcium currents have been reported in sensory neurones. We cannot state unequivocally which high-threshold calcium current component was enhanced by CGRP. However, based on the observation that CGRP increased a transient but not the slowly inactivating high-threshold calcium current, we believe the peptide enhanced primarily the N-type calcium current component. 4. CGRP increased the maximal peak current and caused a modest negative shift of < or = 10 mV in the peak of the current-voltage (I-V) relation in three of six neurones. In the remaining three neurones the peptide increased the maximal peak current without a detectable shift in the peak of the I-V relation. 5. To determine if the CGRP-induced enhancement in calcium current was associated with an increase in calcium conductance, we studied the effect of the peptide on the instantaneous current-voltage (I-V) relation when currents were evoked at a clamp potential (Vc) of +30 mV, positive to the observed maximal current (Vc = 0 to +10 mV). CGRP increased the maximal conductance 23 +/- 4%. 6. The enhancement of calcium current by CGRP was not due to a shift in the voltage dependency of steady-state inactivation of the calcium channels. The stimulatory effect of CGRP on calcium current was evaluated by evoking currents from different holding potentials (Vh) at the same Vc (+10 mV). CGRP-induced increases in calcium currents were similar over the range of (Vh) from -60 to -110 mV, suggesting that the peptide did not alter voltage-dependent steady-state inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)
Wiley
J W
JW
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109.
Gross
R A
RA
MacDonald
R L
RL
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009475:Neurons, Afferent / Q000378:metabolism*; D009620:Nodose Ganglion / Q000378:metabolism; D037342:Pertussis Toxin; D051381:Rats; D018003:Receptors, Calcitonin; D011956:Receptors, Cell Surface / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000378:metabolism*
D015220:Calcium Channels; D018003:Receptors, Calcitonin; D011956:Receptors, Cell Surface; D010566:Virulence Factors, Bordetella; D006160:Guanosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D015740:Calcitonin Gene-Related Peptide; D000109:Acetylcholine; D002118:Calcium