[Role of calcium in the mechanism underlying the inhibitory effect of streptomycin on carotid sinus baroreflex in rats].

ABSTRACT

The effect of streptomycin (SM) on carotid baroreflex was examined in 23 anesthetized rats with isolated carotid sinus perfusion. The results obtained are as follows. (1) In response to perfusion with SM (200 micromol/L), the functional curve of carotid baroreflex was shifted to the right and upward with a decrease of peak slope (PS) and a reflex decrease in mean arterial pressure (RD)(P<0.01), indicating an inhibitory effect of SM on carotid sinus baroreflex. (2) By perfusing the isolated carotid sinus with high Ca(2+) solution (4 mmol/L), the inhibitory effect of SM on carotid baroreflex was partially eliminated. The functional curve of SM was shifted to the left and downward with PS increasing from 0.27+/-0.04 kPa to 0.37+/-0.02 kPa (P<0.01) and RD was enhanced from 4.32+/-0.14 kPa to 6.18+/-0.17 kPa (P<0.01). On the other hand, the threshold pressure (TP) and saturation pressure (SP) were significantly decreased from 10.29+/-0.29 kPa to 9.98+/-0.33 kPa (P<0.05) and from 27.26+/-0.42 kPa to 25.22+/-0.38 kPa (P<0.05), respectively. (3) By pretreatment with Bay K 8644 (500 nmol/L), an agonist of calcium channels, the effect of SM on carotid baroreflex was completely abolished. (4) Exposure of the carotid sinus to SM following pretreatment with charybdotoxin (ChTX,100 nmol/L), a blocker of the Ca(2+)-activated K(+) channel (KCa), still inhibited the baroreflex. These results suggest that the inhibitory action of SM on carotid baroreflex may be mediated by suppressing Ca(2+) influx.