Effect of the potassium channel opener ZM260384 on skeletal muscle function during restricted blood flow in the anaesthetized cat

Abstract

The aim of the present experiment was to determine whether the potassium channel opener 2-(2,2-bis(difluoromethyl)-6-nitro-3,4-dihydro-2H-1,4-benzoxazine-4-yl)pyridine -N-oxide (ZM260384) was capable of accelerating the decline in skeletal muscle function during restricted blood flow in vivo. Cats (3.0-4.5 kg body weight) were anaesthetized with alphaxalone-alphadalone and breathed spontaneously following tracheotomy. Isometric tension was measured in the extensor digitorum longus-anterior tibialis (EDL-TA) muscle group. Ischaemia was induced by perfusing the hindlimb with the animal's own blood at a rate of 12.5 ml min-1 using a roller pump and stimulating the common peroneal nerve to induce repetitive submaximal tetanic contractions in the EDL-TA. The number of stimulation voltage increments required each minute to maintain a constant level of submaximal mechanical output and the time to exhaustion were used as indices of the rate of tension decline. The rate of tension decline in the ischaemic EDL-TA in the presence of 2M260384 at 3 mg kg-1 a maximally hypotensive dose predicted to be within the dose range required to exert direct effects on skeletal muscle, was measured and compared with the rate of tension decline in the presence of ZM260384 at 0.03 mg kg-1, also a maximally hypotensive dose but below the predicted dose range for skeletal muscle effects. The number of voltage increments per minute was 1.93 ± 0.07 and 1.48 ± 0.14 (P < 0.05) in the presence of 3 and 0.03 mg kg-1 2M260384, respectively. Time to exhaustion was 1.75 ± 4.2 and 7.2 ± 0.8 min (P < 0.05) in the presence of 3 and 0.03 mg kg-1 Zm260384, respectively. Given that there was no difference between these two groups in any haemodynamic variable measured, the results of the present study suggest that ZM260384 (3 mg kg-1) increases the rate of isometric force loss in ischaemic skeletal muscle in vivo.