AbstractsEarth & Environmental Science

Control of slow wave frequency in cat small intestinal muscle was investigated with microelectrodes. Exposure of intact muscle or isolated longitudinal muscle to low Ca('2+) saline decreased slow wave frequency with less than a 6 mV change in resting potential. This frequency decline was characterized by a prolongation of the diastolic phase of the slow wave. Raising Ca(,0)('2+) to 2-3 times normal increased slow wave frequency. At Ca(,0)('2+) greater than 4 times normal, the slow wave frequency again decreased. However, this decrease in frequency was characterized by a prolongation of the systolic phase of the waveform. Application of Ca conductance blockers (Co('2+), Mn('2+), D600, verapamil), increasing Mg(,0)('2+) or increasing internal pH decreased slow wave frequency by a prolongation of the diastolic region of the slow wave. Addition of db-cAMP to Krebs saline made hypertonic with sucrose or decreasing internal pH increased slow wave frequency. These results indicate a relationship between internal Ca('2+) and the pacemaker of slow wave frequency. A scheme is proposed to explain that relationship.