Recent studies have indicated that the pH-sensitive tandem-P domain K+ channel TASK-1 is present in central neurones including cerebellar granule neurones, and that its inhibition by various transmitters represents an important mechanism to regulate neuronal excitability (Millar et al. 2000; Brickley et al. 2001). Since TASK-1 is inhibited by acute hypoxia in rat type I carotid body cells (Buckler et al. 2000), we investigated the effects of acute hypoxia on the TASK-1 current in acutely isolated rat cerebellar granule neurones. Cell isolation and culture were as previously described (Ramsden et al. 2001), and perforated patch recordings were employed. Animals were humanely killed according to Schedule 1 methods. The standing outward K+ current (TASK-1; Millar et al. 2000; Brickley et al. 2001) was studied using voltage ramps (800 ms duration, from -20 to -100 mV, 0.05 Hz). Current amplitudes (means ± S.E.M.) reported were obtained at -20 mV and statistical analysis was performed using Student’s paired t tests.
Reducing the perfusate pH from 7.4 to 6.4 caused a reversible reduction in current density from 80.9 ± 0.5 to 20.6 ± 0.2 pA pF-1 (P < 0.001), corresponding to 75 ± 2 % inhibition. Currents were also reversibly inhibited by 47 ± 3 % (P < 0.001) in the presence of anandamide (1 µM), and by 55 ± 1 % (P < 0.001) in the presence of 100 µM carbachol. In four cells studied, reducing the PO2 of the perfusate from ca 150 mmHg to ca 30 mmHg also reversibly inhibited TASK-1 currents by 47 ± 3 % (P < 0.001). Importantly, during current inhibition by either anandamide (n = 4) or pH 6.4 (n = 4), hypoxia failed to reduce current amplitudes further, indicating these agents all acted on the same conductance.
Our results indicate that TASK-1 is an O2-sensitive K+ current in cerebellar granule neurones. Since this current exerts important influences on neuronal excitability our results provide a likely contributory mechanism underlying hypoxic/ischaemic hyperexcitability (Lipton, 1999).
L.D.P. is an MRC scholar.