Effect of whole-body potassium depletion on plasma, erythrocyte, and middle gluteal muscle potassium concentration of healthy, adult horses

Abstract

SUMMARY The effects of whole-body potassium depletion induced by food deprivation on plasma, erythrocyte, and middle gluteal muscle K concentrations was quantified in 16 healthy, adult horses before, during, and at the end of a 7-day period of food deprivation during which water and sodium chloride were available ad libitum. Potassium concentrations were determined by atomic absorption spectroscopy. Plasma K concentration remained constant (3.49 ± 0.09 mM K/L of plasma; mean ± sem) throughout the study. Erythrocyte potassium concentration decreased from 93.10 ± 1.94 mM K/L of erythrocytes on day 0 to 88.63 ± 2.39 mM K/L of erythrocytes on day 2 (decrease of 4.8%; P < 0.05) and thereafter did not change. The K concentration of the middle gluteal muscle decreased from 91.06 ± 2.96 μM K/g of muscle (wet weight) to 79.61 ± 2.09 μM K/g of muscle (decrease of 12.6%; P < 0.05) on day 4 and decreased further on day 7 to 73.62 ± 1.85 μM K/g of muscle (decrease of 19.2%; P < 0.05). There was no correlation between the plasma and erythrocyte K concentrations (r = −0.066), the erythrocyte and middle gluteal muscle K concentrations (r = 0.167), or the plasma and middle gluteal muscle potassium concentrations (r = −0.018). The water content of the middle gluteal muscle remained constant (73.23 ± 0.36%) throughout the study. Erythrocyte membrane potential did not change (−99.26 ± 0.87 mV) during the study, whereas the magnitude of the membrane potential of the middle gluteal muscle decreased from −105.84 ± 1.67 mV on day 0 to −100.93 ± 2.10 mV on day 7 (P < 0.05).