Activation of potassium(K+)cu rrents plays a critical role in the control of prog rammed cell death Because pituitary adenylate cyclase-activating polypeptide(PACAP)has been shown to inhibit the apoptotic cascade in the cerebellar cortex du ring development, we hav einvestigated the effect of PACAP on K’cu rrents in cultu red cerebellar g ranule cells using the patch-clamp technique in the whole-cell configu ration Two types of outward K_cu rrents, a transient K+cu rrent(k)and a delayed rectifier K’cu rrent(/K)were characterized using two different voltage protocols and specific inhibitors of K’channels Application of PACAP induced a reversible reduction of the /K amplitude, but did not affect/A, while the PACAP-related peptide vasoactive intestinal polypeptide had no effect on either types of K+ cu rrents Repeated applications of PACAP induced g radual attenuation of the electrophysiological response In the presence of guanosine 5'-rthio1rlphosphate(GTPh, S), PACAP provoked a marked and i rreversible/K depression, whereas cell dialysis with guanosine 5'-bthiodiphosphate GDPl3S totally abolished the effect of PACAR P re-treatment of the cells with pertussis toxin did not modify the effect of PACAP on/K In contrast, cholera toxin suppressed the PACAP-induced inhibition of/K Exposu re of g ranule cells to dibutyryl cyclic adenosine monophosphate(dbcAMP)mimicked the inhibitory effect of PACAP on/K Addition of the specific protein kinaseAinhibitorH89inthepatch pipettesolution preventedthe reductionof/Kinducedbyboth PACAPand dbcAMR PACAPprovoked a sustainedincreaseofthe restingmembranepotentialin cerebellarg ranule cells cultu red eitherin high orlowKCI-containingmedium, and this long-ferm depolarizing effect of PACAP was mimicked by the/K specific blocker tetraethylammonium chloride fTEA)In addition, pre-incubation of g ranule cellswithTEA suppressedthe effect of PACAP on resting membrane potential TEAmimickedthe neu roprotective effect of PACAP against ethanol-induced apoptotic cell death, and the increase of caspase-3 activity observed after exposu re of g ranule cells to ethanol was also significantly inhibited by TEA Taken together, the present results demonstrate that, in rat cerebellar g ranule cells, PACAP reduces the delayed outward rectifier K’cu rrent by activating a type 1 PACAP(PACl)receptorcoupledtothe adenylyl cyclase/protein kinaseApathwayth rougha choleratoxin-sensitiveGsprotein Our dataalso showthat PACAP and TEA induce long-term depolarization of the resting membrane potential promote cell su rvival and inhibit caspase-3 activity, suggesting that PACAP-evoked inhibition of/K contributes to the anti-apoptotic effect of the peptide on cerebellar granule cells

We have investigated the effects of sigma ligands [1,3-di(2-tolyl)guanidine (DTG) and (1)-pentazocine] on the electrical activity of cultured frog pituitary melanotrope cells by using the patch-clamp technique. DTG and (1)-pentazocine (10 mM each) induced a reversible depolarization associated with an increase in membrane resistance and action potential firing. In voltage-clamp experiments, DTG and (1)-pentazocine elicited inward currents whose intensity augmented with membrane depolarization. The currents vanished or reversed between -90 and -100 mV, at values close to the K1 equilibrium potential(EK15 -102 mV). DTG (2–500 mM) and (1)-pentazocine (0.2-200 mM) reduced the outward delayed rectifier K1 current [IK(V)] in a dose-dependent manner with EC50 of 64 and 37 mM,respectively. In contrast, naloxone (50 mM) and pirenzepine (10mM) did not affect the sigma ligand-induced inhibition of IK (V).Addition of guanosine-59-O-(3-thiophosphate) in the pipettesolution irreversibly sustained the DTG-induced current whereas guanosine-59-O-(2-thiodiphosphate) virtually suppressed the response. Cholera toxin-pretreatment (1 mg/ml; 18hr) abolished the inward current and the inhibition of IK (V)induced by sigma ligands. In contrast, pretreatment with pertussis toxin (1 mg/ml; 18 hr) had no effect. Taken together, these data indicate that DTG and (1)-pentazocine activate the electrical activity of cultured frog melanotrope cells by reducing both a tonic K1 current and a voltage-dependent [IK (V)] K1conductance through the activation of a cholera toxin-sensitive G-protein.