Bicarbonate and fast-twitch muscle: Evidence for a major role in pH regulation

Abstract

Internal pH (pHi) was analyzed in rat extensor digitorum longus (Edl) muscle at 30 degrees C with single-barrel liquid ion-selective electrodes. Average pHi in 284 cells was 7.197 +/- 0.006. Increases in CO2 from nominally 0 to 5% produced an acidification from which recovery took place. In different groups of cells, recovery from the 5% CO2 acidification was significantly inhibited by 100 microM 4,4' diisothiocyanatostilbene 2,2' disulfonic acid (DIDS), Cl removal, Na removal and 2 mM amiloride. Prepulsing with 20 mM NH4 in the presence of CO2/HCO3 typically reduced pHi to only about neutral, whereas 50 mM reduced pHi to 6.7-6.8. In the nominal absence of CO2/HCO3, 20 mM NH4 reduced pHi to about 6.7 from which recovery took place at about 58% of the rate seen in different cells in the presence of CO2/HCO3. In the presence of CO2/HCO3, cells prepulsed with 50 mM NH4 had fully recovered to an average pHi of 7.22 +/- 0.04 about 90 min after removal of NH4. However, 90 min after removal of 20 mM NH4 in the absence of CO2/HCO3, average pHi was significantly less (7.05 +/- 0.03). Intrinsic buffering capacity (beta i) was obtained during pulses of CO2, acetic acid or after an NH4 pulse. beta i was significantly reduced in the absence of HCO3, Cl or Na and HCO3. The data provide significant support for an important role of HCO3 in the control of pHi in fast-twitch muscle.

Extracellular carbonic anhydrase activity facilitates lactic acid transport in rat skeletal muscle fibres

“…Therefore, they were combined to yield a mean value of 35 ± 4 mM ∆pH _1 for EDL (n = 14) and of 86 ± 16 mM ∆pH _1 for soleus (n = 14). This value of BF non-HCO 3 for the EDL is much lower than the value reported by Grossie et al (1988) (100 mM ∆pH _1 ). Therefore, BF non-HCO 3 was also measured under the conditions of Grossie et al (1988), using 25 mM Hepes-100 % O 2 (= 0 % CO 2 ) and 24 mM HCO 3 _ -5 % CO 2 .…”

“…This value of BF non-HCO 3 for the EDL is much lower than the value reported by Grossie et al (1988) (100 mM ∆pH _1 ). Therefore, BF non-HCO 3 was also measured under the conditions of Grossie et al (1988), using 25 mM Hepes-100 % O 2 (= 0 % CO 2 ) and 24 mM HCO 3 _ -5 % CO 2 . This resulted in a value of BF non-HCO 3 of 83 ± 4 mM ∆pH _1 (n = 3) for EDL and 107 ± 6 mM ∆pH _1 (n = 3) for soleus.…”

Correlation of lactate and pH in human skeletal muscle after exercise by 1H NMR

“…Grossie el al. ( 18) suggested that in fast twitch muscle, the putative (Na)HCO;/Cl transporter is important in H + transport since pHi recovery from NH 4' prepulses is substantially slowed in the absence of COZ / HCO j . As a consequence, a fiber type specificity of the distribution of the NaH and (Na)HCO:I/Cl exchangers was proposed.…”

Cloning, Tissue Distribution, Genomic Organization, and Functional Characterization of NBC3, a New Member of the Sodium Bicarbonate Cotransporter Family

“…The relative contribution of each process varies with cell type, the metabolic requirements of the cell, and local environmental conditions. Intracellular pH regulatory processes that have been characterized functionally in skeletal, smooth muscle, and cardiac cells include: Na ϩ /H ϩ exchange (1-3, 9 -22), Na(HCO 3 ) n cotransport (12,13,16,17,21,(23)(24)(25)(26)(27)(28)(29), Na ϩ -dependent (12,18,19,26,30,31) and -independent (19,24,26,29,32,33) Cl Ϫ /base exchange, and lactate/ proton cotransport (3).…”