Objective:To assess the predominant subtype of calcium channel present in neurons of the paracervical ganglia (PG) of the female rat and the ability of neuroactive peptides to modulate total calcium current.
Methods:Whole-cell patch clamp techniques were used on isolated PC neurons to assess clacium current modulation in the presence and absence of selective calcium channel subtype inhibitors and neuropeptides. Digital imaging analysis of cells was used to determine neuronal cell size distributions within the ganglia.
Results:Average PG cell diameter was 28.1 μm. Most PG neurons (64%) had an N-type calcium current that contributed 41% of the total calcium current. The low voltage-activated or T-type current was not present. Very few neurons (22%) were sensitive to the P-type calcium channel blocker ω-agatoxin IVA, and in only 10% of neurons was the calcium current sensitive to the L-type channel blocker nimodipine. Neuropeptide Y (NPY) inhibited the calciumm current by 41% in 79% of the neurons, but vasoactive intenstinal peptide (VIP) had no effect. Calcitonin gene-related peptide (CGRP) both increased and decreased the calcium current in separate cell populations.
Conclusions:Calcium currents in female rat PG neurons are carried primarily through N-type calcium channels with a small contribution from L- and P-type channels. An unidentified calcium channel type is also present. Modulation of the calcium current by NPY is demonstrated, and support for the presence of a local, CGRP-mediated circuit is presented.
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