Journal of Neurophysiology, Vol 62, Issue 1 119-125, Copyright © 1989 by APS
Effects of ionic calcium on the responses of canine testicular polymodal receptors to algesic substances
J. Sato, K. Mizumura and T. Kumazawa
Department of Nervous and Sensory Functions, Nagoya University, Japan.
1. To explore possible mechanisms of the responses to algesic substances
(bradykinin, hypertonic saline, and high K+ solution) of polymodal
receptors in the canine testis, the Ca2+ concentration was varied in vitro.
2. After 1 min in Ca2+-free media, the responses to both high K+ solution
(60 mM K+) and hypertonic saline (0.6 M Na+) were significantly augmented
and tended to increase further with time; return to normal Ca2+
concentration quickly reversed these changes. These augmenting effects were
blocked by the substitution of Mg2+ for Ca2+. The excitation produced by 60
mM K+ was decreased by increasing Ca2+ in a concentration-dependent
fashion. 3. Reducing the bath concentration of K+ decreased responses
evoked by 9 X 10(-8) M bradykinin (BK), whereas increased K+ concentration
had the opposite effect. 4. The excitatory effects of BK were significantly
suppressed in extracellular Ca2+-free condition. The suppression was not
affected by the addition of Mg2+. Prostaglandin E2, which has been known to
be released by BK and to augment the BK response, failed to restore the
suppressed response by either preapplication (2.8 X 10(-7) M) or
simultaneous application in high concentration (1.4 X 10(-5) M). 5. On the
basis of these observations, it was postulated that Ca2+
concentration-dependent changes of the responses to 60 mM K+ and 0.6 M Na+
results from Ca2+-dependent "membrane surface potential" changes. The
suppressed response to BK by Ca2+ depletion may be explained by the
intervention of Ca2+-dependent processes other than PG production.
