Physiological control of the heart and pH balance in Antarctic fish: An adaptation to cold temperatures

Changes in temperature are thought to affect the relative contributions of the excitatory adrenergic and inhibitory parasympathetic nerves to the vertebrate heart. Investigations of the heart function in the extreme case of Antarctic fish was conducted to determine/interpret the effects of temperature on the heart. ECG electrodes were implanted in a free swimming fish (Pagothenia borchgrevinki and Trematomus bernacchii) and recorded the chronotropic (rate) changes with activity and temperature. Differentiation between the adrenergic and cholinergic inputs to the heart were determined by blocking one or the other with propranolol or atropine. To differentiate between the chronotropic and inotropic responses a force displacement transducer was applied to an in situ perfused heart of a decerebrated fish to assess the principal control mechanism of heart function in Antarctic fish and to ascertain the effects of temperature change. Related to this aspect of metabolic control is the regulation of the acid-base balance of the blood. Blood pH regulates oxygen delivery to tissues in Antarctic fish. Temperature and activity may change the acid-base balance. Evaluation of the acid-base status were made from blood bicarbonate concentration calculated from pH and CO2 measurements in the blood using a blood micro analyser. The content of fixed metabolic acids (principally lactic acid) in the blood at different temperatures and levels of activity was measured.