Light-dependent ion influx into toad photoreceptors.

To measure the influx of Na+ and other ions through the light-dependent permeability of photoreceptors, we superfused the isolated retina of the toad, Bufo marinus, with a low-Ca2+ (10(-8) M), low-Cl- Ringer's solution containing 0.5 mM ouabain. Under these conditions, the membrane potential of the rod is near zero and there is no light-induced potential change either in the rod or in more proximal neurons. The photoreceptors, however, continue to show a light-dependent increase in membrane resistance, which indicates that the light-sensitive channels still close with illumination. Dark-adapted retinas show a larger 22Na+ accumulation than do light-adapted retinas. The extra accumulation of 22Na+ into dark-adapted retinas can be removed if the retinas are washed in darkness with low-Ca2+ Ringer's solutions, or if the ionophore gramicidin D is present in the perfusate. The additional accumulation in dark retinas corresponds to a flux of at least 10(9) Na+ per receptor per second, which is close to the value of the photoreceptor dark current. The light-dependent uptake of 22Na+ can be prevented by exposing the retinas to Ca2+ during the incubation period, but is restored if the phosphodiesterase inhibitor IBMX is added to the perfusate. A significant light-dependent ion accumulation can be observed for the cations K+, Rb+, Cs+, and Tl+, in addition to Na+, but not for methylamine, choline, or tetraethylammonium

Sarcoptic mange in wombats

Sarcoptic mange, commonly referred to as scabies, is a cosmopolitan disease affecting seven different orders within the class Mammalia. It is caused by the mite Sarcoptes scabiei (Linnaeus, 1758) Latreille, 1802 which is an obligate parasite of the skin. The mite is typically oval shaped, dorsally rounded and ventrally flattened. Its length varies between 200 and 500 μm depending on its life-cycle stage. Of the Australian marsupials, only wombats and the koala (Phascolarctos cinereus) (Vombatiformes) and the common ringtail possum (Pseudocheirus peregrinus) (Pseudocheiridae) have been reported with sarcoptic mange. In wombats, sarcoptic mange has been reported as the major infectious disease affecting the group, although it mainly occurs in only one of the three species, the common wombat (Vombatus ursinus). In this species sarcoptic mange can be debilitating. Several reports of severe sarcoptic mange in common wombats describe animals as emaciated and lacking hair with a thick dry crust, composed of keratin, many mites and their debris, bacteria and neutrophilic debris adherent to the skin (Figure 1). This crust is similar to that found in domestic animals with hyperkeratotic sarcoptic mange and humans with Norwegian scabies. The thick crust may be fissured by the movement of the wombat (Figure 2). The underlying skin may also crack resulting in haemorrhage, pyoderma and sometimes cutaneous myiasis. This may encompass the entire body with the head, neck, shoulders and limbs more commonly affected. Typically, the epidermis is thickened and there is a mild predominantly mononuclear inflammatory infiltrate in the dermis. In some animals hypersensitivity reactions occur towards Sarcoptes, with few mites present in the skin. Intense pruritus, a characteristic sign of hypersensitivity reactions to Sarcoptes in humans and animals has been reported in wombats with sarcoptic mange. Only occasional outbreaks of sarcoptic mange have been recorded in the southern hairy-nosed wombat (Lasiorhinus latifrons) and the disease has not been reported in the northern hairy-nosed wombat (Lasiorhinus krefftii)