Rate of pressure change and hyperbaric bradycardia in the mouse sinus node

Sinus node preparations from mice were hydraulically compressed at 10, 100, and 500 atm x min-1 in Tyrode's solution at 27 degrees C. At the highest compression rate, both a delay and a more pronounced beating frequency response to pressure was seen. The delayed reaction is ascribed to either adiabatic effects or a time-delay in conformational changes in the pacemaker cell membrane. The potentiating effect of a high compression rate could be eliminated by autonomic blockade (atropine and practolol).