Effects of ionic calcium on the responses of canine testicular polymodal receptors to algesic substances.
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.
Department of Nervous and Sensory Functions, Nagoya University, Japan.
J
J
Sato
K
K
Mizumura
T
T
Kumazawa
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D015232:Dinoprostone / Q000494:pharmacology; D004285:Dogs; D008274:Magnesium / Q000502:physiology; D008297:Male; D009431:Neural Conduction; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012462:Saline Solution, Hypertonic; D013094:Spermatozoa / Q000294:innervation; D013737:Testis / Q000187:drug effects / Q000294:innervation / Q000502:physiology*
D012462:Saline Solution, Hypertonic; D008274:Magnesium; D015232:Dinoprostone; D011188:Potassium; D001920:Bradykinin; D002118:Calcium