PROPERTIES OF THE RYANODINE RECEPTOR PRESENT IN THE SARCOPLASMIC-RETICULUM FROM LOBSTER SKELETAL-MUSCLE

Microsomal sarcoplasmic reticulum (SR) fractions from lobster skeletal muscle were found to bind [H-3]-ryanodine. [H-3]-ryanodine binding wa s enhanced by AMP, Ca2+ and caffeine, and significantly diminished by ATP, Ba2+ and Sr2+. Furthermore, dantrolene and ruthenium red, two cla ssical inhibitors of Ca2+ release from the SR, blocked [H-3]-ryanodine binding. Similarly, tetracaine, known to block the charge movement as sociated with excitation-contraction coupling in vertebrate muscle, in hibited the binding of the alkaloid. Our lobster SR preparation exhibi ted a single high-affinity ryanodine binding site (K-d = 6.6 nM, B-max = 10 pmol/mg protein). Since SDS-PAGE of the SR proteins revealed a m ajor band c. 565 kDa which comigrated with the putative ryanodine rece ptor from both rat and chicken skeletal muscle, we concluded that lobs ter skeletal muscle is equipped with the 565 kDA ryanodine receptor. F inally, incorporation of the SR microsomal fraction from lobster into planar bilayer membranes revealed the presence of a ryanodine-sensitiv e Ca2+ channel activity (160 pS in symmetrical 200 mM CsCl solutions). We concluded that both the crustacean and vertebrate skeletal muscle ryanodine receptor share the relevant properties such as molecular wei ght and affinity for ryanodine and inositol 1,4,5 triphosphate. Howeve r, there are important differences between the two receptors including differential effects of the alkaloid on the Ca2+ release channel and modulation of the receptor by nucleotides.