Direct effects of the hyperglycemic factor of the freshwater snail Lymnaea stagnalis on isolated glycogen cells

Abstract

In the freshwater pulmonate snail Lymnaea stagnalis special cells, the glycogen cells (GC) are present for the storage of glycogen reserves. These cells occur in large numbers in the anterior mantle region. In a previous paper in vitro experiments with intact anterior mantle tissue indicated that a hyperglycemic factor is released from the central nervous system (CNS) which stimulates glycogen mobilization in mantle tissue ( M. A. Hemminga, J. J. Maaskant, W. Koomen, and J. Joosse (1985). Neuroendocrine control of glycogen mobilization in the freshwater snail Lymnaea stagnalis. Gen. Comp. Endocrinol. 57, 117–123). In the present study the question of whether this factor affects glycogen metabolism of GC isolated from mantle tissue was investigated. It is reported that in high-K + Ringers the CNS is stimulated to release a factor which, in a dose-dependent way, inhibits glycogen synthesis in isolated GC (measured as a decreased incorporation of [ 14C]glucose into glycogen). Simultaneous with this glycogen synthesis-inhibiting effect, stimulation of glycogen degradation is found (measured as a decreased retention of prelabeled glycogen). It is concluded that (1) the factor released by the CNS having these effects on isolated GC is the same as the hyperglycemic factor which was reported to stimulate glycogen mobilization in intact mantle tissue, and (2) GC after isolation from mantle tissue have retained their ability to respond to this factor. High-K + bathing Ringers of the cerebral/buccal ganglia have a stronger inhibiting effect on glycogen synthesis in isolated GC than bathing Ringers of the remainder part of the CNS, indicating that in this part of the brain the major release sites of the hyperglycemic factor are located. Dorsal body hormone, ovulation hormone, or growth hormone of L. stagnalis probably are not identical with the hyperglycemic factor, as homogenates of parts of the cerebral ganglia which are known to contain these respective hormones do not influence glycogen synthesis in isolated GC.