Two types of PG cells can be distinguished by the presence of delayed-rectifier. R-type has DR current and shows outward rectification under current-clamp; N-type does not. A third type, X-type, has properties of both R- and N-type. Zinc modifies the A-type current, but not the delayed-rectifier type: at given voltages, it reduces A-current peak amplitude, slows its kinetics. Zinc shifts activation and inactivation toward more positive voltage. Thus, at physiological resting potential -55mV, zinc accelerates repolarization.