Carbonic anhydrase inhibitors ameliorate the symptoms of hypokalaemic periodic paralysis in rats by opening the muscular Ca2+-activated-K+channels

Carbonic-anhydrase inhibitors are effective in channelopathies possibly by opening the Ca2+-activated-K+channels. However, the in vivo effects of these drugs in K+-deficient rats, the animal model of familial hypokalaemic periodic paralysis(hypokalaemic-PP), are currently unknown. Measures of insulin-responses, serum electrolytes levels and patch-clamp experiments were therefore performed in K+-deficient rats treated in vivo with dichlorphenamide (DCP), ethoxzolamide (ETX), hydrochlorthiazide (HCT), methazolamide (MTZ), bendroflumethiazide (BFT) and acetazolamide (ACTZ). Ten days treatments of K+-deficient rats with DCP, BFT, ETX and ACTZ (5.6 mg/kg per day) restored the serum [K+] to control values and prevented the insulin-induced paralysis. In ex vivo experiments, the carbonic-anhydrase inhibitors enhanced the activity of Ca2+-activated-K+channels with the order of efficacy: ACTZ>BFT>ETX>DCP. In contrast, HCT and MTZ failed to stimulate the Ca2+-activated-K+channels and to prevent the hypokalaemia and paralysis. At the concentration of 1 mg/kg per day, all these drugs failed to ameliorate the hypokalaemic-PP symptoms. The activation of Ca2+-activated-K+channel in addition to the mild diuretic effect explained the efficacy of ACTZ and DCP in K+-deficient rats and in familial hypokalaemic-PP.