Abstract

It has been argued that a rise in free, unbound intracellular magnesium (Mg²⁺_i) could be beneficial during myocardial ischemia, effecting the regulation of certain enzymes, the rectification of channels as well as intracellular Na⁺ and Ca²⁺. Mg²⁺ is a cofactor of the Na/K-ATPase, it competes with Ca²⁺ at the contractile apparatus etc. However, all of these properties are confined to the intracellular site. The present study investigates the effect of pH upon intracellular concentrations of Mg²⁺. Here we studied Mg²⁺_i with Mg²⁺-selective microelectrodes (ETH 7025) in isolated guinea pig papillary muscle. Free intracellular Mg²⁺_i in guinea pig papillary muscle was 0.73 ± 0.08 (n = 7, ± SEM) in the same type of tissue. These values are similar to those assessed earlier in sheep Purkinje fibre and ferret papillary muscle. In the present experiments we also changed extracellular pH from 7.4 – 6.4 and back to 7.4. In the same experiments, pHi has been measured using a pH-sensitive microelectrode in order to assess the change of pHi brought about by changing extracellular pH. This manoeuver led to a change of pHi from a resting level of 7.19 ± 0.03 (n = 7, ± SEM) to 6.81 ± 0.06 (n = 7, ± SEM). These changes of pH_i led to a small but consistant rise of intracellular Mg²⁺. In 7 experiments Mg²⁺_i rose by 0.19 ± 0.06 mM (± SEM) from an initial value of 0.73 ± 0.21 mM. The small rise of Mg²⁺_i is likely to result from ionized Mg²⁺ being liberated from the Mg-ATP complex. Interestingly, despite pH had remained low, after about 7 min Mg²⁺_i returned to normal levels. This observation indicates that intracellular regulation of Mg²⁺_i is slow but operational at even very small changes of Mg²⁺_i suggesting that Mg²⁺_i levels are regulated within a very narrow band in order to guarantee its multifaceted intracellular biological activity.

Author Details

Authors

• S. Gasser
• E. Scherr
• R. Gasser

Departments

• WG of Experimental Cardiology, Department of Cardiology, University Department of Internal Medicine, Graz, Austria

Address

Prof. R. Gasser, MD, DPhil (Oxon)
WG of Experimental Cardiology, Department of Cardiology, University Department of Internal Medicine, Auenbruggerplatz 15, 8036 Graz, Austria
Email: [email protected]

Citation