THE CYCLIC AMP-DEPENDENT PROTEIN-KINASE CATALYTIC SUBUNIT SELECTIVELY ENHANCES CALCIUM CURRENTS IN RAT NODOSE NEURONS

1. The whole‐cell variation of the patch clamp technique was used to study the effect of the purified catalytic subunit of the cyclic AMP‐dependent protein kinase (A kinase catalytic subunit: AK‐C) on the calcium current components of acutely dissociated rat nodose ganglion neurones. 2. The transient low‐threshold calcium current component (T) was stable during whole‐cell recording. In contrast, currents containing the transient high‐threshold (N) and slowly inactivating high‐threshold (L) current components declined steadily after stabilization of the currents during the first 5‐7 min of recording. When AK‐C was included in the recording pipette at physiological concentrations (50 micrograms/ml, approximately 1 microM), currents containing the N‐ and L‐components increased in magnitude beginning 7‐9 min after patch rupture, but there was no effect on the isolated T‐current. The current‐voltage relation of the T‐current component was similar to controls, but the current‐voltage relation for the N‐ and L‐current components was shifted slightly to more depolarized clamp potentials (Vc), approximately 10 mV. 3. The effect of AK‐C on currents containing the N‐ and L‐currents was concentration dependent. There was no effect of 0.1 microgram/ml AK‐C, the lowest concentration tested. Currents evoked from holding potentials (Vh) = ‐80 mV increased 5‐10% during a 20 min recording in the presence of 1 microgram/ml AK‐C and 30‐35% in the presence of 50 micrograms/ml AK‐C. In contrast, currents evoked from Vh = ‐40 mV increased 5‐10% in the presence of either 1 or 50 micrograms/ml AK‐C. The increase in current magnitude was associated with an increased rate of current inactivation and was evident particularly in currents evoked from Vh = ‐80 mV. 4. These effects were blocked by prior incubation of AK‐C (1 microgram/ml) with a specific peptide inhibitor (protein kinase inhibitor peptide, PKIP; 0.2 mg/ml). 5. We evoked calcium currents using very long (1 s) voltage commands and modelled the traces using a multiexponential function in order to determine the effects of AK‐C on the N‐ and L‐current components. The (curve‐fitted) N‐ and L‐current components each declined approximately 50% during a 20 min recording in control neurones.(ABSTRACT TRUNCATED AT 250 WORDS) © 1990 The Physiological Society