Type of Electrical Stimulation Influences Diaphragm Response to Adrenoceptor and Calcium Channel Modulators: the Role of Extracellular and Intracellular Calcium Events

Abstract

Abstract. The influence of direct single pulse and subtetanic electrical stimulation (ES) on isolated rat hemidiaphragm response to adrenoceptor antagonists and calcium channel blockers was investigated. Muscle contractility was stimulated by cumulative micromolar noradrenaline. Noradrenaline effects on developed tension (Td) in the presence of various α-and β-adrenoceptor antagonists (e.g., prazosin and ICI 118551) were qualitatively different during different types of ES. Also, intact L-voltage calcium channels were necessary for noradrenaline-induced potentiation of Td during both types of ES, while the balance between ryanodine receptors-and inositol triphosphate (IP 3 )-related calcium events in the muscle was influenced by the pattern of the ES.

β‐Adrenergic modulation of skeletal muscle contraction: key role of excitation–contraction coupling

“…First, Ca 2+ channel blockers antagonize the β‐adrenergic potentiation of force in amphibian fibres (Williams & Barnes, b ) and rat diaphragm (Varagić & Kentera, ; Todorović et al . ), but not in rat limb muscle (Cairns & Dulhunty, b ). Also, the positive inotropic effect is magnified in the presence of Ca 2+ ionophores in rat diaphragm (Varagić et al .…”