Calcium and magnesium sensitivity of the carotid baroreceptor reflex in cats

The systemic blood pressure response to changes in carotid sinus pressure has been examined during variations in the calcium and magnesium concentration of the perfusate of the isolated sinus. The threshold for the blood pressure response was increased by 16 +/- 0.8% when calcium was raised from 1.1 mM (control) to 2.2 mM and increased by 27 +/- 1.8% when calcium was raised to 3.3 mM. The threshold was reduced by 21 +/- 0.7% in zero calcium and 13 +/- 0.8% in 0.55 mM Ca2+. The sensitivity (slope of the linear portion of the pressure response curve) of the reflex was not significantly changed except at 3.3 mM Ca2+ where it was reduced by 16 +/- 2.9%. Magnesium had directionally similar effects of a lesser magnitude. Earlier work described the reduced sensitivity and threshold of the baroreceptor reflex when sodium concentration in the carotid perfusate was reduced. The present study shows that reducing calcium attenuates the effect of lowered sodium and increasing calcium augments it. These results are discussed in terms of possible ionic influences on the receptor potential and spike generation.