Electrotonic and chemical effects on minimal gradient requirements for cardiac muscle

¹ Department of Physiology, State University of New York Downstate Medical Center, Brooklyn, New York

The thresholds to rectangular pulses and the minimal gradient requirements for excitation of trabecular muscles from dog hearts were determined. Catelectrotonus lowered thresholds and shortened the minimal gradient or lambda (). Anelectrotonus raised thresholds and greatly prolonged lambda. Low calcium lowered threshold and increased lambda, whereas high calcium raised the threshold and shortened lambda. Quinidine and dinitrophenol had little effect on threshold but prolonged lambda. Cyanide also had little effect on threshold but shortened lambda. Urethan and cocaine slightly raised thresholds and shortened lambda. There is thus no correlation between changes in threshold and changes in minimal gradient (). The significance of lambda is not known.