Effect of saliva from horse fly Hybomitra bimaculata on kinetic properties of Na, K-ATPase: possible role in regulation of relaxation

Abstract

Effect of saliva from horse fly [Hybomitra bimaculata] on kinetic properties of Na, K-ATPase: possible role in regulation of relaxation

The possible involvement of salivary gland extract (SGE) from horse flies in modifying hyperpolarization and relaxation via alterations in functional properties of sarcolemmal Na, K-ATPase in the host tissue was tested [in vitro] by application of various amounts of SGE from [Hybomitra bimaculata].

SGE in the amount of 3 μg proteins representing approximately the equivalent of one salivary gland of [Hybomitra bimaculata] induced a stimulatory effect on Na, K-ATPase at all ATP concentrations applied. This effect resulted from the improved ATP-binding site affinity in the Na, K-ATPase molecule, as implicated by the reduction in K[M]. Increasing the amount of SGE to 6.5 μg resulted in inhibition of the enzyme, which was characterized by reduction in V[max] and also K[M]. This suggests that in the presence of relatively high [Hybomitra bimaculata] SGE concentration some SGE components affect Na, K-ATPase, when ATP is already bound to the enzyme.

Our results indicate that SGE from the horse fly [Hybomitra bimaculata] contain at least two different biologically active compounds modifying the acute recovery and maintenance of excitability during contractile activity in the host tissue by affecting Na, K-ATPase with opposite effects, depending on the ratio of SGE-proteins to proteins of the host tissue. [PUBLICATION ABSTRACT]