Figure 7.

cAMP effects on GIRK isoforms. (A) Original current trace recorded at −80 mV from an oocyte expressing m₂R and GIRK1. GIRK currents are therefore produced exclusively from the GIRK1/GIRK5 heterooligomeric assembly. cAMP was injected during basal HK current. (B) Current trace recorded from an oocyte expressing GIRK1/GIRK2 channels (endogenous GIRK5 was knocked out with the KHA2 antisense oligonucleotide). cAMP was injected during ACh superfusion. (C) Same as in B, but the oocyte expressed homooligomeric GIRK2 channels. (D) Effect of antisense oligonucleotide (KHA2) coinjected with either GIRK1 or GIRK1/GIRK4 cRNA on I_ACh currents. Calculated average values ± SEM are shown; the number of individual cells is given in parenthesis. (* and ***) Mean value deviates significantly (P < 0.05 and 0.001) from the corresponding control group (KHA2 not coinjected). (E) Statistics of cAMP effects on various GIRK subunit combinations on basal I_HK currents as well as on agonist-induced currents (I_ACh). Calculated average values ± standard error of the effect normalized to basal I_HK produced by the GIRK1/GIRK4 combination of a given experimental day are shown; the number of individual oocytes are in parenthesis. (** and ***) Mean value of the experimental group deviates significantly (P < 0.01 and 0.001) from zero.