Chilling-injury and disturbance of ion homeostasis in the coxal muscle of the tropical cockroach (Nauphoeta cinerea)

Adults of warm- and cold-acclimated tropical cockroaches, Nauphoeta cinerea were exposed to low temperatures of 0 or 5 °C for various time intervals (hours to days). Development of chilling-injury (defects in crawling and uncoordinated movements) and mortality during the exposure were assessed and correlated with the changes in concentrations of metal ions (Na+, K+ and Mg2+) in the haemolymph and coxal muscle tissue. Warm-acclimated insects entered chill-coma at both low temperatures. In their haemolymph, the [Na+] and [Mg2+] linearly decreased and [K+] increased with the increasing time of exposure. The rate of concentration changes was higher at 0 than at 5 °C. The concentration changes resulted in gradually dissipating equilibrium potentials across the muscle cell membranes. For instance, EK decreased from − 49.8 to − 20.7 mV during 7 days at 5 °C. Such a disturbance of ion homeostasis was paralleled by the gradual development of chilling-injury and mortality. Most of the cockroaches showed chilling-injury when the molar ratio of [Na+]/[K+] in their haemolymph decreased from an initial of 4.4 to 2.1–2.5. In contrast, the cold-acclimated cockroaches did not enter chill-coma. They maintained constant concentrations of ions in their haemolymph, constant equilibrium potentials across muscle cell membranes and the development of chilling-injury was significantly suppressed at 5 °C for 7 days.