Contractile properties of skeletal muscle fibre bundles from mice deficient in carbonic anhydrase II

Abstract

The function of cytosolic carbonic anhydrase (CA) isozyme II is largely unknown in skeletal muscle. Because of this, we compared the in vitro contractile properties of extensor digitorum longus (EDL) and soleus (SOL) fibre bundles from mice deficient in CA II (CAD) to litter mate controls (LM). Twitch rise, 1/2 relaxation time and peak twitch force at 22 degrees C of fibre bundles from CAD EDL [28.4+/-1.4 ms, 31.2+/-2.3 ms, 6.2+/-1.0 Newton/cm(2) (N/cm(2)), respectively] and CAD SOL (54.2+/-7.5 ms, 75.7+/-13.8 ms, 2.9+/-0.5 N/cm(2), respectively) were significantly higher compared to LM EDL (20.5+/-2.2 ms, 21.9+/-3.7 ms, 4.5+/-0.2 N/cm(2)) and LM SOL (42.8+/-3.5 ms, 51.4+/-2.4 ms, 2.1+/-0.4 N/cm(2)). However, in acidic Krebs-Henseleit solution, mimicking the pH, PCO(2), and HCO(3) (-) of arterial blood from CAD mice, twitch rise, 1/2 relaxation time, and peak twitch force of fibre bundles from CAD EDL (19.3+/-0.7 ms, 19.7+/-2.3 ms, 4.8+/-0.8 N/cm(2)) and CAD SOL (41.4+/-3.6 ms, 51.9+/-5.5 ms, 2.2+/-0.7 N/cm(2)) were not significantly different from LM fibre bundles in normal Krebs-Henseleit solution (EDL: 19.7+/-1.1 ms, 21.6+/-0.6 ms, 4.7+/-0.2 N/cm(2); SOL: 42.5+/-3.1 ms, 51.8+/-2.6 ms, 1.8+/-0.3 N/cm(2)). A higher pH(i) during exposure to acidic bathing solution was maintained by CAD EDL (7.37+/-0.02) and CAD SOL (7.33+/-0.05) compared to LM EDL (7.28+/-0.04) and LM SOL (7.22+/-0.02). This suggests that the skeletal muscle of CAD mice possesses an improved defense of pH(i) against elevated pCO(2). In support of this, apparent non-bicarbonate buffer capacity (in mequiv H(+) (pH unit)(-1) (kg cell H(2)O)(-1)) as determined by pH microelectrode was markedly increased in CAD EDL (75.7+/-4.1) and CAD SOL (85.9+/-3.3) compared to LM EDL (39.3+/-4.7) and LM SOL (37.5+/-3.8). Both latter phenomena may be related to the slowed rate of intracellular acidification seen in CAD SOL in comparison with LM SOL upon an increase in PCO(2) of the bath. In conclusion, skeletal muscle from mice deficient in CA II exhibits altered handling of acid-base challenges and shows normal contractile behavior at normal intracellular pH.