Calmodulin-dependent cyclic nucleotide phosphodiesterase activity is altered by 20 microT magnetostatic fields

Absorbance measurements at 660 nm of calmodulin (CaM) dependent cyclic nucleotide phosphodiesterase activity under cell free conditions indicate that 30-min exposures to weak magnetostatic field intensities alters this activity, compared to zero magnetic field exposures. This effect depends nonlinearly on the concentration of free calcium, with maximum magnetic interaction apparently occurring at an optimal Ca(2+) concentration corresponding to 50% activation (EC(50)). If one regards Ca(2+)/CaM activation as a switching process, then increasing the magnetic field at Ca(2+) levels in excess of optimal acts to bias this switch towards lower calcium concentrations. A magnetic dependence has been previously reported by others in an homologous system, CaM dependent myosin light chain phosphorylation, implying that there may be an underlying magnetic interaction that involves the initial Ca(2+)/CaM binding process common to both enzymatic pathways. The level of magnetostatic intensity at which this effect is observed ( approximately 20 microT) implies that CaM activation may be functionally sensitive to the geomagnetic field.